Function useWeekAndDayIndices

packages/@react-spectrum/s2/src/Calendar.tsx:766–790

* Calculate the week index (0-based) and day index (0-based) for a given date within a month in a * calendar. * * @param date - The date to calculate indices for. * @param locale - The locale string (e.g., 'en-US', 'fr-FR', 'hi-IN-u-ca-indian'). * @param firstDayOfWeek - Optional override for t

(date: CalendarDate, locale: string, firstDayOfWeek?: DayOfWeek)

 * @returns Object with weekIndex and dayIndex.
 */
function useWeekAndDayIndices(date: CalendarDate, locale: string, firstDayOfWeek?: DayOfWeek) {
  let result = useMemo(() => {
    // Get the day index within the week (0-6)
    const dayIndex = getDayOfWeek(date, locale, firstDayOfWeek);

    const monthStart = startOfMonth(date);

    // Calculate the week index by finding which week this date falls into
    // within the month's calendar grid
    const monthStartDayOfWeek = getDayOfWeek(monthStart, locale, firstDayOfWeek);
    const dayOfMonth = date.day;

    const weekIndex = Math.floor((dayOfMonth + monthStartDayOfWeek - 1) / 7);
    const lastDayOfMonth = startOfMonth(date).add({months: 1}).subtract({days: 1});
    const lastWeekIndex = Math.floor((lastDayOfMonth.day + monthStartDayOfWeek - 1) / 7);

    return {
      weekIndex,
      lastWeekIndex,
      dayIndex
    };
  }, [date, locale, firstDayOfWeek]);

  return result;
}